In conventional diagnostic radiography, an object is placed between an x-ray radiation source and a detector and the relative positions of the source and detector are positioned for proper alignment and angle for obtaining an image. When the object is an arm, leg, or chest of a patient, the x-ray tube and the detector are visible to the x-ray technician and can be easily aligned.
Alignment is more difficult for dental or intraoral radiography. The detector position is within the patient's mouth and is not visible to the technician. Instead, the technician typically places the detector into some type of holder, and then inserts the holder into place in the mouth. The holder may have a bite plate or other type of supporting member that helps to position the detector appropriately. As is well known, holders of this type can be cumbersome and uncomfortable to the patient. Holders and other positioning devices are not error-proof, and positioning errors with these devices can mean that the images obtained are not suitable for diagnosis. Poorly aligned detectors can be the cause of problems such as cone cuts, missed apices, and elongation and related angulation or parallax errors, for example. These alignment problems can result in re-takes, additional image captures to acquire an acceptable image. Re-takes are undesirable due to the additional x-ray radiation exposure to the patient and prolonged patient discomfort with the sensor in the mouth.
Conventional x-ray sources have included aim 1ndicators that help the technician adjust the position and angle of the x-ray source. Often these aim indicators use visible light to trace an outline that helps to center the radiation beam. These work well where the radiation detector can be seen, but fall short of what is needed where the detector is not visible, such as with intraoral imaging. The technician must guess or estimate both the position of the intraoral sensor and the angle of incidence of x-rays on the sensor.
The simplified schematic of FIGS. 1A and 1B show how mis-alignment between an x-ray source 10 and a detector 20 can occur. In these examples, x-ray source 10 provides visible light aim 1ndices 12 used for aim centering. When correct aim alignment is achieved, shown at example (a), detector 20 is centered, as shown within aim 1ndices 12. Aim 1s incorrect at examples (b) and (d).
For best imaging results, proper alignment with respect to angle, or angulation, is also needed. Incident radiation from x-ray source 10 is preferably orthogonal to detector 20 as shown in example (a). Line N in FIG. 1 indicates a normal, or orthogonal line, to the surface of detector 20. Examples (c) and (d) show incorrect angular alignment. In example (c), aim 1s correct but angulation is incorrect. In example (d), both aim and angulation are incorrect. In example (e), detector 20 is rotated in plane.
It is instructive to note that the schematic examples of FIGS. 1A and 1B assume an orthogonal positioning of x-ray source 10 to detector 20. In some embodiments, an oblique orientation may be used.
One proposed solution to the problem of positioning an intraoral sensor relative to the x-ray source is described in U.S. Patent Application Publication No. 2009/0060145 entitled “POSITIONING ADJUSTMENT OF A MOBILE RADIOLOGY FACILITY” by Tranchant et al. The apparatus described in Tranchant et al. '0145 uses an arrangement of electromagnetic emitters, such as radio frequency (RF) emitters, in cooperation with a sensor (reception unit) to determine the position and angle of an intraoral detector with respect to an x-ray source. Mis-alignment can then be reported to the operator on an operator console or display screen.
The solution proposed in the Tranchant et al. '0145 disclosure can detect and report mis-alignment for intraoral radiography and can minimize or eliminate the need to use cumbersome positioning devices within the patient's mouth. However, some practical difficulties remain. The technician needs information in order to correct for mis-alignment and to verify that proper alignment has been obtained. Conventional methods for reporting the alignment information, such as providing information on an operator console, for example, can be difficult to use when making position adjustments. The technician needs to move back and forth between the operator console and the x-ray tube, checking and correcting each adjustment until proper alignment is achieved.
Thus, there is a need for an apparatus and method for providing improved alignment of the radiation source and image detector in intraoral radiography.